Drying device



Jan. l2, 1932.- N; TESTRUP E1' AL 1,840,857

DRYING DEVICE U Filed Feb. 27. 1929 2 Sheets-Sheet l Jan. 12, 1932. N.TEsTRUP ET AL' l 1,840,857

nanna DEvI'cE Filed Feb. 27. 1929 2 sheets-sheet 2 15 ly high PatentedJian. 1.2, .1932

UNITED STATES PATENT OFFICE NILS TESTRUP, OLOF SODERLUND, AND THOMASGRAM, OF LONDON, ENGLAND, AS- SIGNORS T TECHNO-CHEMICAL LABORATORIES,LIMITED, LONDON, ENGLAND DRYING Application led. February 27, 1929,Serial No.

This invention relates to the drying of materials which are. wholly'carried in or by gaseous medium and to which heat is imparted frompartition surfaces in proximity to which the material is moved.

In drying devices thus employing heating surfaces through which the heatfor the drying is transmitted the economy of the drier depends largelyupon the cost of the heat- 1o ing surface per unit output and in drierswhich are employed for example in the lignite industry the cost of theheating surface per unit output is so high that the driers cannot beworked economically unless a relativetemperature difference is employedsay 1n the neighbourhood of 40o C. or upwards.

In the British Patent No. 286,743, there is described a drier where thecost of heating surface per unit output is considerably reduced andlower temperature dierences say about 20 C. become economical and in theBritish Patent No. 294,289 there is described how as a consequencemultiple effect drying can be obtained.

The object of the present invention is to provide drying devices inwhich the heating surface per unit of output will represent a,

much lower cost and in which for example lower temperature differences,say of about 5 to 10 C., become realizable economically,

the cost of single effect driers can be greatly reduced, multiple eectdrying becomes even more advantageous, and it becomes practica- 85 bleto employ the thermo-compressor in driv ers for obtaining high thermalefficiency.

When drying fine coal, powdered lignite,

peat powder and other materials in the above manner by carrying them byand suspended 0 in a gaseous medium through tubes heated on the outside,we discovered that by increasing the weight of material carried per unitof gaseous medium we could increase the rateV of evaporation per unit ofheating surface and when investigating the cause of this increase wefound that when blowing the material through the tubes'the bulk of themai terial would travel in the centre of the tube and that bymcreasingthe quantity of material present we increased the number of DEVICE343,097, and in Great Britain March 1, 1928.

particles travelling in closeproximity to the heating surface. We alsofound that the larger particles, which take a longer time to drythan thesmaller-ones, were travelling near the centre and therefore were at thelongest distance from the heating surface.

vThe invent-ion consists in a drying device employing the gaseous mediumsuspension method for transmitting heat to the material to be dried'inwhich the particles of material are subjected to forces which cause themto maintain a close relationship with the heattransmitting surfaces.

The invention further consists in giving to the gaseous medium in whichthe material to be dried is carried,'an impulsecausing the material totravel along or closely adjacent to the heating surface and not in thecentre -of the tube.

The invention further consists in carrying out drying processes inaccordance with either of the preceding paragraphs and in arranging forthe material and the gaseous medium to have a rotating movement whiletravelling through the tubes, so as to keep the material closelyadjacent to the heating surfaces.

The invention further consists in carrying out drying processes-inaccordance withany of the preceding paragraphs and in arranging forexample by using spirally rifled tubes for the heating surface tosubject the particles of material to centrifugal force and keep j themin contact with or close proximity to the tube Walls while travellingtherein.

The invention also consists in improvements in or relating to dryingdevices and processes carried out therein as hereinafter described. vReferring now to the accompanying drawings l Figure 1 shows a dryingapparatus containing a drier having tubes in accordance rwith theinvention;

Figure 2 shows to a larger scale a short.5l length of one tube;

Figures 3, 4, 5, 6 and 7 show alternative forms of the cross section ofdrying tubes in accordance with the invention.

In carrying the present invention into effect in one way we employinstead of ordinary cylindrical tubes tubes which have spiral groovesextending all or the greater part of the length for example in themanner in which they are disposed in a ride barrel. rlhis, due to theaction of the centrifugal forces set up, causes the material to travelalong in contact with or closely adjacent to the interior surfaces ofthe tubes and considerably increases the evaporation per unit of heatingsurface.

in the drying apparatus shown in Figure l a is a fan which. is driven bythe pulley a and draws a current of air through pipe b into whichdisintegrated material which is to be dried is delivered. through thebranch connection b by means of a feed screw b2.

The fan a delivers the current of air in which the material to be driedis carried to y the tubes l: of the drier c, a flaring :mouth piece c2being provided at the outlet of the fan so that the material-ladencurrent of air may be uniformly divided up between all the tubes of thedrier.

The drier consists of a cylindrical or other casing oin which isprovided a plurality of tubes hereinafter more fully described and thespace surrounding the tubes in the casing is fed with heating medium asfor example steam, water or the like which enters at the pipe Z andleaves by the pipe d.

The tubes 0 although shown. of limited length in the drawing are of anylength which may be desirable to perform the drying operation and thecurrent of air carrying the dried material leaves the drier by the pipereducing outlet e and bend by which. it is led into the cycloneseparator g from which the separated dried material is collected fromthe outlet la while the current of air freed from the material leaves bythe outlet j'.

The tubes c of which a short length is shown to a larger scale in Figure2 are provided with spiral grooves it or equivalent means formaintaining a spiral motion of the material-laden air throughout thefull length of the tubes and the grooves or their equivalent may beformed in a variety of different ways.

Figure 3 shows a tube formed from two half sections Z, Z each. of whichrepresents a D shape with the central portion of the straight part Iofthe outline cutaway and the faces of the vremaining parts Z2, Z3 of thestraight portions joined together as by brazing or other suitabletreatment, the two sections being helical so that when joined asdescribed there is formed a cylindrical tube with the internal fins Z2,Zs extending in a helical direction throughout the length of the tubes.

Figure 4 shows a tube m having longitudinal indentations m', m2 uponopposite sides thereof, the indentations running the full Leanser lengthof the tubes and being helically or spirally disposed throughout thelength in the same manner as the fins in the tube last described.

Figure 5 shows a square or rectangular section tube n in which thecorners n, n2, n3 and n4 are slightly rounded and the tube is given ahelical twist as in the other cases.

Figure 6 shows another tubular section 0 somewhat similar to the tube mbut with the l indentations less pronounced and taking more the form offlattened 4sides o', o2.

Figure 'i' shows a tube p having six indentations p which are as in theother tubes disposed in a helical or spiral direction throughout thelength of the tubes.

The spirally grooved or riiied tubes may be produced in any convenientmanner which will provide the grooving preferably without alteration inthe normal thickness of the walls of the tubes or the like employed; forinstance tubes might be drawn with spirally disposed grooves orprojections upon the walls thereof or such grooves or projections mightbe produced by rolling or other convenient processes. Multi-sidedtubular elements having a twisted or spiral configuration may also beemployed and suitably modified at the ends for conveniently fastening intube plates or the like.,

rlhe foregoing arrangement also ensures that the larger particles makethe greatest amount of contact with or are maintained in closestproximity to the heating surfaces and thus they obtain the greatersupply of heat necessary for their drying and a .more uniform drying ofthe whole of the material is edected.

When divided material is carried in suspension along a tube by a currentof ,fluid the friction with the walls creates eddy currents or whirlswhich result in a greater proportion of the material being in the centrepart of the iiuid than in the surroundingportion and the object of thehelical distortions is to create by a spiral motion of the fluid suf;-

ficient centrifugal force to overcome this centre seeking effect on theparticles. helices must, therefore, be so proportioned that a sufficientcentrifugal action isobtained without undesirably adding to the wallfriction effect.

A s shown in the drawings the pitch of the helix is about eight timesthe tube diameter which is substantially correct for some materials. lnother cases, however, somewhat shorter pitches may be employed providedthe foregoing requirementsI are complied' with. l.

An impulse can be given to the particles or a force may be imposed uponthem lby any other suitable means having regard to the nature of thematerial tol be dried and to the circumstances of each case; for examplebaf- The i es or other deformations of the tubes and similar means maybe employed.

With the low temperature differences made possible when Working inaccordance with this invention it may be desirable to employ thethermo-compressor in connection with such drying devices and to raisethe temperature of the evolved vapours suiiciently by .compression toemploy them upon the other side of the heat-transmitting partitions asthe heating medium.

It is to be understood that the constructions hereinbefore described aregiven by Way of. example only and the arrangement showing the passage ovair and material through the drier may ent ways. V

Modications and additions of other kinds may also be introduced Withoutin any Way departing from the spirit of this invention.

We claim:

1. Apparatus for drying nely divided material comprising means forinducing a streamv of fluid charged with the material to be dried, meansdirecting said charged stream into a plurality of extended conduits,helical distortions in the entire length of the Walls of said conduitsmaking an angle of more than 45 with a circumferential line on ity ofextended conduits, yhelical distortions in the entire length of thewalls of said conduits of a pitch at least exceeding four diameters orcreating rotation without transverse eddy movement of the fluid in eachcondult and tovobtain by centrifugal action close contact of thesuspended material with the walls thereof, and means for heating theWalls of said conduits from' the exterior.

In testimony whereof We have signed our names to this specification.

NILS TESTRUP. OLOF SODERLUND. THOMAS GRAM.

be modified in ldiffer- .the conduit Walls, and means for heating theWalls of said conduits-from the exterior.

2. Apparatus for drying finely divided material comprising means forinducing a stream of luid charged With the material to be dried carriedin suspension therein, means directing said charged stream by gradualincreases of cross-sectional area into a plural.- ity of tubularconduits, twoihelical distortions diametrically opposed in the entirelength of the Walls of said conduits making an angle of more than 45with a circumferential line on the conduit Walls, and means for heatingthe walls of said conduits from the exterior.

3. Apparatus for drying finely divided material comprising means forinducing a stream of fluid charged with the material to be dried carriedin suspension therein, means directing said charged stream by gradualincreases of cross-sectional area into a plurality of tubular conduits,helical distortions in the entire length of the walls of said conduitsdisposed at a smaller angle to a plane containing a tubev axis than to aplane at right angles thereto for creating rotation without transverseeddy movement of the fluid in each conduit, and means for heating thewalls of said conduits from the exterior.

4. Apparatus for drying finely divided material comprising means forinducing a stream of fluid charged with the material to be dried carriedin suspension therein, means directing said charged stream by gradualincreases of cross-sectional area into a plural-

